The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Gear pumps and gerotor pumps are often the preferred choice for a fixed or positive displacement pump in applications requiring flows and pressures of low to medium nominal values. One drawback of such pumps, however, is their efficiency. Due to their construction, there is backflow or leakage through the meshing rotors and around the ends of the rotors when they are operating which results in reduced forward flow and thus reduced pumping efficiency.
Fixed displacement vane pumps perform in the same flow and pressures ranges and exhibit improved efficiency due to reduced leakage and backflow. Such reduced leakage and backflow are the result of better sealing between the outer edges of the vanes and the walls of the rotor cavity. However, since contact between the pump vanes and pump cavity and thus the seal quality is primarily the result of centrifugal force and line pressure acting on the center of the rotor, both of which push the vanes outward to seal on the wall of the pump cavity, the seal quality improves with higher rotational speeds and higher line pressure and degrades with lower speeds and lower line pressure. This aspect of vane pump operation is especially problematic at startup of an unprimed pump. Since at startup, the pump will typically be operating at reduced speed and zero pressure, seal quality is low and this problem in exacerbated by the unprimed state of the pump such that establishment of priming and delivery of pressurized fluid may take an undesirably long period of time.
The present invention provides a solution to the dual problems of startup of an unprimed vane pump.